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Automatic Chicken Door

Introduction

My wife and I started raising chickens this year. A few days after we moved them out to the coop, the novelty of going out in the morning to let them out and in the evening to lock them up began to wear off. We needed an automatic door opener! Being an engineer, and a cheapskate, I decided to build one myself rather than shell out over $200 for a commercial one (of questionable quality). I can do questionable quality myself, thank you very much.

The design I settled on was to use the motor from a cordless screwdriver and put a spool on it to wind up a thin rope that would lift the door. To control the door, I modified the electrical parts of the screwdriver to interface with two limit switches to control the up/down travel. Since we already had the lights in the coop on a timer, I used this switched power to control when the door would open and close.

In addition, to increase the security of the door against being opened at night (by raccoons, etc) I fashioned an automatic mechanical latch that bolts on to the door. This prevents the door being opened except if it is lifted by the opener.

If you decide to use my design to build an opener please let me know! I hope others can make use of this design to save them some time and money. Also feel free to email me with any questions, comments or suggestions.

Before I get into the details of the design, here is a video of the door in operation.

Materials

Here is a list of what I used to construct the opener. Some items I already had on hand so no price is listed. Most of these could be substituted with a similar item or with one that better suits your particular needs.

Thin Rope - I used some twine but something like parachute cord would be better

Hose Clamps

Spool - I used a spool from a roll of plumbing solder. Anything similar in size would work.

Mechanical Components

First step is to disassemble the screwdriver so you can remove the back half where the battery and switch is located. For this screwdriver you will need to open the front half case first in order to remove the back half. Cut the wires leading to the motor, leaving enough to work with later. You should end up with something like this:

Screwdriver motor with electrical parts removed. (Click to enlarge)

For the spool I found a nearly empty roll of plumbing solder and used the plastic spool from that. To mount it on the motor I found a socket from the screwdriver kit that fit the inside of the spool well and superglued the socket in to the spool. I then just used the socket adapter to plug it into the output shaft of the motor. When you have it working well, you may want to superglue the socket to the adapter, and the adapter into the motor. Since the motor runs at about 200 rpm, you can’t really go much larger than about 1″ inside diameter on the spool. Anything larger would make the door move too fast or overload the motor.

Motor mounted in coop with spool attached. (click to enlarge)

Electrical Components

The circuitry of the screwdriver is very simple. Inside you will find a battery, a small circuit board with the charger connector, two resistors and an LED, and a forward/reverse switch. The switch is not used in this design, cut it off leaving plenty of wire on the circuit board and discard it.

Here is an electrical schematic of the opener. Click to enlarge in new window:

Electrical Schematic (click to enlarge)

The operation of the circuit is pretty simple. The charger for the screwdriver is plugged into a circuit that has power when we want the door to be open. The 5v DC in from the charger is used to control a dual pole, dual throw relay. This relay acts to change the direction of the motor. Coop lights on, relay energized, motor runs “up.” Coop lights off, relay not energized, motor runs “down.” A diode is added between the circuit board and the battery to prevent the power from the battery from energizing the coil when the charger is off. There are two limit switches to control where the door stops when it is going up/down.

So let’s start hooking the circuit up. You’ll need some basic soldering skills for this. If you’ve not soldered before, don’t worry, look up some soldering tutorials on google or youtube and practice on a few scraps of wire first.

Before you start remove the battery from the battery connector and set it aside.

The first step is to solder the wires from the battery connector to the relay. They will go on the middle set of the 6 pins.

Then, solder a wire from the battery negative pin to one of the coil pins. Solder another piece of wire to the other coil pin, this will be the power that energizes the coil with +5v.

Relay with the battery and coil terminals connected. (click to enlarge)

Next, we’ll work on the circuit board. First, solder the other end of the coil +5v wire to the circuit board as shown. Be careful that no bare wire touches the other areas on the board.

Coil +5v wire soldered to circuit board. (click to enlarge)

Then, we need to add the diode in between the circuit board and the battery. You can cut the red wire and splice the diode in, or you can remove the wire from the circuit board and replace it with the diode, and then attach the wire to the other end of the diode. I chose the second method. The band on the diode indicates polarity and must face toward the battery.

Diode installed on board with battery wire connected to diode. Band faces toward battery (away from board). (click to enlarge)

Next, we will wire up the limit switches. Make sure to use enough wire to allow for mounting the switch away from the motor. The switches I used can be wired as either Normally Open or Normally Closed. Which way is necessary will depend on where you plan to mount the switches in relation to the door. The up limit needs to be closed when the door is down or partway down, and open when it reaches the top. The down limit needs to be closed when the door is up or partway down, and open when it reaches the bottom. For my setup, I used an NC switch for the top limit and an NO switch for the bottom. I bent the ends of the switch lever to make it glide over the door more easily.

Switch wired normally open

Switch wired normally closed, with bent lever.

Next, connect the motor and the limit switches to the relay. On the 6 switch terminals, the motor negative wire is soldered to the upper left terminal and then a jumper is installed from that terminal to the lower right. The motor + wire is connected to the black wire from both limit switches, soldered and taped. The red wire from the top limit switch is connected to the lower left pin on the relay. The red wire from the bottom limit switch is connected to the top right pin on the relay.

Relay wiring complete. (click to enlarge)

At this point the opener should be operational. Connect the battery to the circuit and test the operation by manually operating the limit switches. Once you are satisfied, tape all the components together with electrical tape to keep them from moving. Make sure none of the wires are putting a lot of force on the solder joints. Remember you need to be able to plug the charger in to the circuit board.

Installing the Opener

Installing the opener will vary depending on the configuration of your coop and your door. Here’s how I did mine:

I mounted the motor to a 2x4 above the door with some hose clamps. The battery and circuitry is zip tied in place next to the motor.(click to enlarge)

I mounted the switches to a piece of OSB to bring them out in front of the door tracks. I adjusted the distance from the door until the switches operated reliably. I had to be careful not to let the door open too far. If it did the arm on the bottom switch would fall below the door and get caught when the door came down. (click to enlarge)

Automatic Latch

The automatic latch consists of a counterweighted lever which pivots to engage a pin beside the door and prevent the door from being opened. Instead of the lift rope being tied directly to the door, the rope is now tied to the top of the lever. When the door is lowered, the motor allows enough slack for the counterweight to tilt the lever and engage the stationary lock pin. When the door is opened agian, the lift rope pulls on the lever, tilting it back to vertical and unlatching the door, and then lifting the door. The adjustment of the bottom limit switch is critical to this working properly. It took me a few tries to get it adjusted just right so the motor would release enough slack for the latch to fully engage, and so that the motor would not be engaged when the door was lifted agianst the latch.

Latch assembly mounted on door. The nail at the left serves as the pin which the lever engages. The counterweight is a chunk of 3/8" steel. (click to enlarge)

Here is a video of the latch in action:

Update - Nov 2009

The door has been working great! I have had a couple problems worth mentioning:

The wall-wart power supply that came with the screw driver failed after about 3 months of use. I found another of the same voltage and spliced the connector on to that, making sure the polarity was right. I had to leave it plugged in overnight before the battery was recharged enough for it to operate. The supply I used was an old Motorola cell-phone power supply.

The other problem I had was the door starting to bind up in the tracks. This would stop it from closing all the way, then the motor would keep running and wrap the cord back around the spool the other direction and open the door back up past the top limit switch jamming it there. Solution was just to bend the tracks slightly so the fit wasn’t as tight.

Thanks for the comments everyone has left. Always nice to hear feedback.